Interrupt Service Thread (IST)

In general, an IST is responsible for:

• performing some kind of servicing of that hardware; usually this is done by simply reading and/or writing the hardware's registers, but may also involve copy data into and/or out-of the hardware
• updating some data structures shared between the IST and some of the threads running in the application
• notifying other driver threads that some kind of event has occurred
• notifying other processes (clients) that some hardware operation has completed

Depending on the complexity of the hardware device, the IST, and the application, some of the above steps may be omitted.

Let's take a look at each step.